| 1 | #ifndef Py_LONGINTREPR_H
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| 2 | #define Py_LONGINTREPR_H
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| 3 | #ifdef __cplusplus
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| 4 | extern "C" {
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| 5 | #endif
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| 6 |
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| 7 |
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| 8 | /* This is published for the benefit of "friend" marshal.c only. */
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| 9 |
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| 10 | /* Parameters of the long integer representation.
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| 11 | These shouldn't have to be changed as C should guarantee that a short
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| 12 | contains at least 16 bits, but it's made changeable anyway.
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| 13 | Note: 'digit' should be able to hold 2*MASK+1, and 'twodigits'
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| 14 | should be able to hold the intermediate results in 'mul'
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| 15 | (at most (BASE-1)*(2*BASE+1) == MASK*(2*MASK+3)).
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| 16 | Also, x_sub assumes that 'digit' is an unsigned type, and overflow
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| 17 | is handled by taking the result mod 2**N for some N > SHIFT.
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| 18 | And, at some places it is assumed that MASK fits in an int, as well.
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| 19 | long_pow() requires that SHIFT be divisible by 5. */
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| 20 |
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| 21 | typedef unsigned short digit;
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| 22 | typedef unsigned int wdigit; /* digit widened to parameter size */
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| 23 | #define BASE_TWODIGITS_TYPE long
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| 24 | typedef unsigned BASE_TWODIGITS_TYPE twodigits;
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| 25 | typedef BASE_TWODIGITS_TYPE stwodigits; /* signed variant of twodigits */
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| 26 |
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| 27 | #define SHIFT 15
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| 28 | #define BASE ((digit)1 << SHIFT)
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| 29 | #define MASK ((int)(BASE - 1))
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| 30 |
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| 31 | #if SHIFT % 5 != 0
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| 32 | #error "longobject.c requires that SHIFT be divisible by 5"
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| 33 | #endif
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| 34 |
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| 35 | /* Long integer representation.
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| 36 | The absolute value of a number is equal to
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| 37 | SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
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| 38 | Negative numbers are represented with ob_size < 0;
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| 39 | zero is represented by ob_size == 0.
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| 40 | In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
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| 41 | digit) is never zero. Also, in all cases, for all valid i,
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| 42 | 0 <= ob_digit[i] <= MASK.
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| 43 | The allocation function takes care of allocating extra memory
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| 44 | so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available.
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| 45 |
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| 46 | CAUTION: Generic code manipulating subtypes of PyVarObject has to
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| 47 | aware that longs abuse ob_size's sign bit.
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| 48 | */
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| 49 |
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| 50 | struct _longobject {
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| 51 | PyObject_VAR_HEAD
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| 52 | digit ob_digit[1];
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| 53 | };
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| 54 |
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| 55 | PyAPI_FUNC(PyLongObject *) _PyLong_New(Py_ssize_t);
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| 56 |
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| 57 | /* Return a copy of src. */
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| 58 | PyAPI_FUNC(PyObject *) _PyLong_Copy(PyLongObject *src);
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| 59 |
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| 60 | #ifdef __cplusplus
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| 61 | }
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| 62 | #endif
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| 63 | #endif /* !Py_LONGINTREPR_H */
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